The method is used to operate a drive train, wherein the operation is directed for example to driving a motor vehicle, in particular to acceleration. The drive train is intended for use in the motor vehicle, so that the invention relates also to a motor vehicle provided with a correspondingly equipped drive train. The drive train is equipped with at least one primary drive axle and the at least one secondary drive axle. These axles are operatively connected or at least can be operatively connected, wherein the transmission torque of the clutch is adjustable, in particular between the primary drive axle and the secondary drive axle via the clutch which transmits the torque.
The transmission torque can be in this case set between a minimum transmission torque and a maximum transmission torque. The minimum transmission torque equals for example zero, but it can be also different from zero, in particular greater than zero. The maximum transmission torque depends usually on the design of the clutch; however, it is preferably at least as large, preferably larger than a drive torque that can be provided by a drive apparatus or a drive assembly of the drive train which is or which should be transmitted via the clutch. The maximum transmission torque is provided for example with a clutch overpressure.
Under a drive torque is preferably to be understood the torque that is in fact applied to the clutch, which can be different from the torque that is generated by the drive apparatus or the drive assembly. This can be the case for example with a transmission that is provided with an operative connection between the drive apparatus and the clutch, in particular a shift transmission, when a transmission ratio that is different from one is present or engaged. For the determination of the torque applied at the clutch should be in this respect taken into account the transmission ratio that is present for example between the drive apparatus or the drive assembly on the one hand and the drive clutch on the other hand.
The primary drive axle is an axle of the drive train or of the motor vehicle which is impacted constantly when a torque that is directed at one of the drives of the motor vehicle by this torque or at least by a part thereof. The secondary drive axle can be impacted selectively by the torque or at least by a portion of the torque. For this purpose is provided the clutch which is present between the primary drive axle and the secondary drive axle. In a first operating state of the clutch, the secondary axle is fully decoupled from the primary axle. Accordingly, the motor vehicle is operated only by means of the primary axle. The transmission of a torque from the primary drive axle to the secondary drive axle therefore does not take place. The transmission torque thus in this case equals zero.
In another operating state of the clutch, the transmission torque is greater than zero so that the transmission torque is transmitted from the primary drive axle to the secondary drive axle. In this case, the secondary drive axle also contributes to the driving of the motor vehicle. The motor vehicle or the drive train is provided according to the present embodiments at least temporarily with a plurality of driven axles, in particular at least with two driven axles, but driving with only axle, namely the at least one primary axle, is also enabled, in particular with exactly one single primary drive axle.
For example, the primary drive is connected permanently and/or rigidly to a drive apparatus of the motor vehicle or of the drive train. The drive apparatus is in this case preferably provided with at least one drive assembly, for example an internal combustion engine, and/or an electric engine, as well as with a starting clutch. The primary drive axle is now in particular operatively connected or can be operatively connected via the starting clutch to the drive assembly, while an operative connection is present between secondary drive axle and the drive assembly preferably only with the primary drive axle, which is to say overall with a clutch that is present as the primary drive axle and the starting clutch, or at least only via the clutch.
The clutch can be for example designed as a friction clutch, in particular as a lamellar clutch, for example a lamellar interlock clutch. The maximum transmissible torque of the clutch is adjusted so that it can be controlled and/or regulated by an actuating mechanism or an actuator. As long as the clutch slip is different from zero, corresponding to a normalized difference between the input and output rotational speed of the clutch, the actually transmission torque will also correspond to the torque set by the actuating mechanism. As long as the clutch slip equals zero, the amount of the actually transmission torque can no longer be determined. Only the maximum of the transmittable torque is known according to the set torque which can be referred to as transmission torque.
If the transmission torque is further increased with an already small clutch slip or with a clutch slip of zero, the transmission torque will be further increased, which is why this is referred to due to the high pressure force on the clutch as a clutch overpressure, in particular in the case of the lamellar clutch. The clutch overpressure is usually provided to prevent or reduce clutch slip, in particular with a rapid change of the load. Similar load changes can occur for example as a result of road changes. However, the clutch overpressure has disadvantages. On the one hand, the actuating mechanism of the clutch uses more energy and generates under certain circumstances noises which can be perceived by the driver as an acoustic burden. Moreover, an unnecessary load is put on the actuating mechanism, which has an influence on its lifespan. Finally, the determination of the torque that is in fact transmitted can be achieved only with a low precision because the range of the values in which it is located is increased.
By decoupling the secondary axle, savings can be realized with respect to the consumption of energy by the drive train. These savings are particularly high when the clutch is provided between the primary drive axle and a cardan shaft of the drive train by means of which the primary drive axle and the secondary drive axle can be mutually connected to each other. With such an arrangement of the clutch, the cardan shaft can be also decoupled from the primary drive axle in addition to the secondary drive axle, so that no losses can occur at this location.
The more frequently only the primary drive axle is driven, which is to say that the secondary drive axle is decoupled from the primary drive axle, the lower will be the collective load or the torque level at the secondary axle. Accordingly, this axle or a secondary train drive provided with a secondary drive axle can have a smaller design, whereby on the one hand the weight of the drive train is reduced, while in addition the construction costs can be also reduced. Overall, decoupling of the secondary drive axle from the primary drive axle thus results in some advantages.
The secondary drive train is provided in addition to the secondary drive axle for example with the cardan shaft and/or with a transmission that is provided between the secondary drive axle and the cardan shaft, for example with a differential gear or with an axle differential gear. The gear can thus include at least one ring gear, which is preferably connected to the cardan shaft or attached to it.
However, the smaller design referred to above of the secondary drive train can lead to vibrations of the drive train, in particular with an acceleration of the motor vehicle, for example from the state when the motor of the vehicle is started.
These drive vibrations can lead to acoustic burdens. Furthermore, they can also have a negative influence on parameters such as climbing ability, trailer load and/or similar parameters. In order to adequately suppress these vibrations of the drive train, for example a Hardy disk in installed. This is referred to in the document GB 497 900.